Why am I getting an extra '- Data' in my hard drive name after upgrade?

I have re-installed a couple of time starting from Catalina on a late 2012 iMac (31,1) and keep getting an extra '- Data' added to the volume names. Initially my drive volumes were 'Macintosh HD' and 'Macintosh HD - Data' and after the OCLP upgrade to Sonoma, they were 'Macintosh HD - Data' and 'Macintosh HD - Data - Data'. To make sure I saved my files, I also previously built an external SSD boot/system drive still on Catalina and named it 'Mac Boot' and 'Mac Boot - Data', and made time machine backups of it.

Later, I had some problems with the Sonoma update (unrelated to this question), erased my internal drive and restored from the time machine backup from the SSD version of Catalina which also set the internal disk name to 'Mac Boot'. Then I upgraded that to Sequoia with OCLP 2.0.2 and Sequoia 15.0.1. And once again got an extra ' - Data' appended to the drive names so they are now 'Mac Boot - Data' and 'Mac Boot - Data - Data'. What am I doing wrong when doing the upgrade to cause this?